1. Field of the Invention
The present invention relates to a film deposition apparatus and a film deposition method.
2. Background Art
Epitaxy or epitaxial growth is often employed in manufacturing semiconductor devices that require relatively thick crystalline films. Examples of these devices include power semiconductor devices such as insulated-gate bipolar transistors (IGBTs) and the like.
Vapor-phase epitaxy, a form of epitaxial growth, requires that the film deposition chamber in which a semiconductor substrate (e.g., a silicon wafer) has been placed be kept at atmospheric pressure (0.1 MPa or 760 Torr) or lower. After the substrate has been heated up to a given temperature, the chamber is supplied with a deposition gas which includes a reactive gas. When the deposition gas reaches the surface of the heated substrate, the reactive gas undergoes thermal decomposition or hydrogen reduction, thereby depositing an epitaxial film on the substrate's surface.
Manufacturing large-thickness epitaxial wafers at a high yield rate requires increasing the film deposition speed, which involves consecutively supplying deposition gas onto the surface of a wafer after the wafer has been uniformly heated. Thus, conventional deposition apparatuses are typically designed to rotate a wafer at high speed, thereby increasing the speed of epitaxial growth (see Japanese Patent Laid-Open No. 2008-108983, as an example).
FIG. 3 is a cross section of a conventional deposition apparatus 200 that employs epitaxial growth.
As illustrated in FIG. 3, the deposition apparatus 200 includes the following components: a chamber 201 having upper and lower sections; a hollow liner 202 located inside the chamber 201 to protect its inner walls; coolant passageways 203a and 203b through which coolant water flows to cool the chamber 201; a gas inlet 204 from which to introduce a deposition gas 225; gas outlets 205 from which to discharge the deposition gas 225 after use; a semiconductor substrate 206 (e.g., a wafer) on which vapor-phase epitaxy is performed; a susceptor 207 for supporting the substrate 206; a heater 208, fixed to a support (not illustrated), for heating the substrate 206; flanges 209 for connecting the upper and lower sections of the chamber 201; a packing material 210 for sealing the flanges 209; flanges 211 used for connection to the gas outlet 205; and packing material 212 for sealing the flanges 211.
The liner 202 is typically formed from quartz. The liner 202 includes a head section 231, and an upper open portion of the head section 231 is provided with a shower plate 220 which serves as a flow straightening vane for uniformly supplying the deposition gas 225 across the top surface of the substrate 206.
The heater 208 is used to heat the substrate 206 while a rotating mechanism (not illustrated), rotates the susceptor 207, thereby also rotating the substrate 206 placed on the susceptor 207. After the substrate 206 has been heated sufficiently, the deposition gas 225, which includes a reactive gas, is fed from the gas inlet 204 into the chamber 201 while the substrate 206 is rotating; the gas 225 flows past the through-holes 221 of the shower plate 220, then moves downwardly inside the head section 231 toward the top surface of the substrate 206. Note that the liner 202 also includes a barrel section 230 inside which the susceptor 207 is placed and that the head section 231 is smaller in inner diameter than the barrel section 230.
After reaching the top surface of the substrate 206, the deposition gas 225 undergoes thermal decomposition or hydrogen reduction, thereby depositing a crystalline film thereon. By-product gases, that is, the resulting gas from the deposition process is discharged from the gas outlets 205 located at the bottom of the chamber 201.
As stated above, the packing materials 210 and 212 are used for sealing the flanges 209 of the chamber 201 and the flanges 211 of the gas outlets 205, respectively. The packing materials 210 and 212 are formed of fluorine rubber and can withstand a temperature of up to 300 degrees Celsius or thereabouts. Via the coolant passageways 203a and 203b cooling the chamber 201, it is possible to cool the packing materials 210 and 212 as well and prevent them from deteriorating due to heat.
During vapor-phase epitaxy onto the substrate 206, the heater 208 heats the substrate 206 up to more than 1,000 degrees Celsius. Depending on the type of epitaxial film to be deposited on the substrate 206, the substrate 206 may need to be heated even up to 1,500 degrees Celsius or higher.
An example of a material to be used for such an epitaxial film is silicon carbide (SiC), which is a promising material for high-voltage power semiconductor devices. The energy gap of silicon carbide is twice or three times as large as those of conventional semiconductor device materials such as silicon (Si) and gallium arsenide (GaAs), and its breakdown electric field is larger than those of conventional materials by approximately one order of magnitude. To form an SiC monocrystalline wafer by growing SiC crystals on a substrate, the substrate needs to be heated up to more than 1,500 degrees Celsius or thereabout. What is more desirable is to heat the entire surface of the substrate uniformly at 1,650 degrees Celsius or higher.
As stated above, when the deposition apparatus 200 of FIG. 3 is used to obtain an SiC monocrystalline wafer by growing SiC crystals on the substrate 206, it is necessary to heat the substrate 206 to a high temperature. Accordingly, when it is necessary to heat the substrate 206 to, for example, 1,650 degrees Celsius, the temperature of the heater 208 needs to be maintained at an even higher temperature, for example, 2,000 degrees Celsius or thereabouts.
The heater 208, located below the substrate 206, is often an electric resistance heater formed from carbon (C) or the like.
However, difficulties are involved in using an electric resistance heater to heat the substrate 206 up to such a high temperature as stated above because the connectors for electrically connecting the heater and electrodes are low in thermal resistance. In other words, it is difficult to apply resistance heating for heating the substrate 206 up to more than 1,500 degrees Celsius.
For this reason, some deposition apparatuses that are designed to obtain SiC monocrystalline wafers are provided with two types of heaters: an electric resistance heater located below a substrate and a high-frequency induction heater located at a chamber side-wall section.
The high-frequency induction heater heats the substrate by the radiant heat resulting from induction heating and plays a complementary role in substrate heating.
The electric resistance heater allows precise temperature control of the substrate and plays a major role in substrate heating while the high-frequency induction heater plays a complementary role. The use of the two types of heaters prevents excessive heating of the electric resistance heater.
However, the use of the high-frequency induction heater, which is located at a chamber side-wall section, creates the following problem: the heating effect of the high-frequency induction heater varies depending on its distance from a substrate to be heated.
Thus, the use of a high-frequency induction heater necessitates the positional and height adjustment of the coils of the induction heater to control its temperature. This renders fine and precise temperature control of the induction heater almost impossible.
Therefore, the use of an electric resistance heater and a high-frequency induction heater results in less precise temperature control of heating means as a whole despite the precise temperature control capabilities of the electric resistance heater.
The present invention has been contrived to address the above issue. An object of the invention is thus to provide a deposition apparatus which has a heater located below a substrate to be heated and another heater located at a chamber side-wall section and uses these two heaters to achieve precise temperature control of the substrate while preventing excessive heating of the heater located below the substrate and also to provide a deposition method using this apparatus.